A coccyx fistula - also called sinus pilonidalis - is an inflammation of the gluteal fold. This is usually caused by hair roots filled with ingrown hair. If a hair grows inwards instead of outwards, broken hair and keratin scales are brought under the skin surface. In this way, small nodules (medical granulomas) are formed which can be inflamed by bacteria.
Coccyx fistula: Causes
One reason for the development of a coccyx fistula can be disturbed hair development. A newly growing hair is not properly pushed out of the hair root. The building material of the hair, keratin, is accumulated in the form of bulbous deposits in the hair root (follicle).
Even if the hair is formed normally, a pilonidal sinus can occur. Namely, when hair breaks and spits itself into the wall of the hair follicle. The follicle fills with broken hair. Loose hair from the back or head can also be massaged into the gluteal fold by the constant movements of the buttocks. The surface structure of the hair, similar to an arrow with a barbed hook, means that once spiked hair gets stuck in the fabric and cannot be removed again by washing.
A third cause can be a phenomenon that can sometimes be seen in already distant fistulas: It seems as if hair had grown directly "underground", probably as a result of a developmental disorder. Also here a coccyx fistula is the consequence.
In any case, the extended hair follicle is always recognizable as a small black dot or as an opening the size of a millimeter. If one sees such a pit, the diagnosis of a coccyx fistula is confirmed.